1.Field of the Invention
The invention relates to an image sensor, and more particularly to an image sensor capable of automatically compensating signal range.
2.Description of the Related Art
A semiconductor image sensor (e.g. a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) sensor), commonly implemented in a camera or a camcorder, is used to convert the visible light images into electronic signals, so as to perform subsequent storage, transmission or display.
Due to the imperfect nature of electronic circuits, an image sensor still has a leakage current (or dark signal) when no light is received. The unwanted dark signal will be combined in useful data signals, and worse, the dark signal cannot be distinguished from the data signal. The combination of the dark signal will sacrifice an image dynamic range, and will reduce the image contrast, thereby reducing the image quality. For example, if a black level is too high, information in a bright area may be lost, and may sacrifice the signal range. Therefore, in order to avoid or calibrate the dark signal, a black level calibration (BLC) is usually performed. The black level calibration can accurately obtain a digital image with the full contrast and tiny details in a dark area.